Dilatation catheters are used in particular for dilating arterial lesions or stenoses in the coronary arteries, when such stenoses threaten to seriously obstruct the flow of blood through the artery. Typically, dilatation catheters are emplaced in the coronary artery stenosis by advancing a guidewire which carries a catheter into the coronary artery, and first advancing the guidewire through the constricted aperture at the stenosis. Then, the dilatation catheter, threaded about the guidewire, is advanced therealong until the balloon of the catheter is positioned within the proper area of the coronary artery, after which the balloon is inflated to dilate the artery wall.
In Bonzel U.S. Pat. No. 4,762,129 a dilatation catheter is disclosed in which the guidewire along which the catheter is advanced is retained in a catheter lumen only at an area near the distal end of the catheter, typically being surrounded by the balloon. Along the rest of the catheter length, the guidewire is free and unconnected to the catheter.
An advantage of this is found in the situation when it becomes necessary to remove the catheter without removing the guidewire. With conventional "over the wire" catheters, it is often necessary in this circumstance to install a guidewire extension on the proximal end of the guidewire prior to withdrawing the catheter, so that the guidewire can at all times be gripped and held in stationary position as the catheter is being withdrawn, to avoid the accidental, partial withdrawal of the guidewire along with the catheter. This is of course undesirable since the distal tip of the guidewire may then be pulled out of the constricted stenosis area of the coronary artery, and thus would require repositioning.
While the guidewire extensions described above are in regular clinical use, they are quite inconvenient since they may have to be four feet long or so, extending and coiling all over the operating room in an inconvenient manner.
With the catheter of the Bonzel patent, the use of a catheter extension may be dispensed with, since the guidewire may be gripped by the surgeon at a position which is lateral to the catheter as the catheter is being withdrawn, since the guidewire is not enclosed in a catheter lumen along most of the length of the catheter. Thus, the catheter can be withdrawn while the guidewire is held in its desired position so that it is not accidentally withdrawn along with the catheter.
Horzewski, et al. U.S. Pat. No. 4,748,982 shows another design of dilatation catheter which can be withdrawn from the patient while leaving the guidewire in a desired position within the patient, without the need for a long guidewire extension. Here also, a large portion of the guidewire is positioned laterally of the catheter rather than within a catheter lumen, so that the catheter may be withdrawn while the guidewire is manually gripped and retained in place. Also, the guidewire can pass through a longitudinal slot 36 defined in the catheter of the Horzewski, et al. patent, as described therein.
Both of the catheters disclosed in the patents cited above exhibit significant clinical disadvantages. For example, conventional, over-the-wire dilatation catheters, where the guidewire occupies a catheter lumen throughout most of its length, are better subject to control of the catheter as it is advanced into the arterial system of the patient. Difficulties are encountered in the tracking of catheters which lack a guidewire passing through the great majority of its length. This complicates and renders more difficult the basic advancement technique of such catheters to their desired point of use within the arterial system of the patient. Generally, dilatation catheters having short guidewire-containing lumens relative to their overall length need to carry some other form of stiffener, such as a metal rod or tube, in order to obtain the minimum standards of trackability and pushability. This adds to the complexity and cost of the catheter structure.
Also, in some clinical situations there may be a need to replace the guidewire rather than the catheter after both have been emplaced. This is very difficult to accomplish with the catheters of the two cited patents.
Accordingly, there is a clinical need for a dilatation catheter which exhibits the advantages of the catheters of the cited patents, but which also exhibits the advantages of conventional, over-the-wire catheters, in that they should be easily controllable due to the presence of the guidewire along most or all of the length thereof, with the desired catheter not requiring a stiff, reinforcing rod or tube as part of the catheter itself. Such a catheter needs to have excellent trackability and pushability, while at the same time it can be replaced without the need of a long, cumbersome catheter extension attached to the distal end of the guidewire.
Also, there is a need for a catheter exhibiting all of these advantages, in which, after emplacement of the catheter, the guidewire can be easily replaced rather than the catheter, if that is desired, but the catheter can also be easily replaced when that is desired.
By this invention, a catheter exhibiting the above advantages is provided. The catheter of this invention is very effective both in clinical utility and flexibility, while remaining of low cost and simple construction.